3d forming objects using high melting temperature polymers

ABSTRACT

A system for forming a multiple layer object, the system including: a spreader to form a layer of polymer particles, the polymer particles having a melting temperature (Tm) of at least 250° C.; a fluid ejection head to selectively deposit a first fusing agent on a first portion of the layer and selectively deposit a second fusing agent on a second portion of the layer, wherein the fluid ejection head does not deposit the fusing agent on a third portion of the layer; and a heat source to heat the first portion and second portion, wherein the first portion is part of the multiple layer object and the second portion is not part of the multiple layer object and the second portion raises a temperature of polymer particles in a subsequent layer.

BACKGROUND

Historically, metal parts, generally machined and/or cast, were used forcomponents in mechanically demanding applications. Machining tended tobe the most expensive due to the cost of a skilled machinist. However,machining was also highly flexible and capable of tight tolerances thatwere difficult to achieve by other methods. The development of automatedand semi-automated machining techniques has reduced the touch time (thetime a machinist was operating a system) and the cost of machiningparts. Swiss machines (historically) and Computer Numerical Control(CNC) have seen increasing adoption as they have been able to automateincreasingly complex machining tasks, with a reduction in per partmachinist time. However, other technologies have emerged that also havethreatened the supremacy of machined metal parts.

Three dimensional printing (forming) of objects is a developingtechnology that uses ejectors and/or material to assemble objects. Whilemachining starts with a block of material and removes material until theobject is formed, three dimensional printing, in contrast, builds thepart up bit by bit until the object is formed. Early three dimensionalprinting used ejected fluid to provide all of the mass of the developingpart. Other methods have used incorporated particles and/or solidmaterial to provide much of the mass of the formed object. Not providingall the material through an ejected fluid has increased the speed andreduced the cost of three dimensional printing. Three dimensionalprinting continues to be a developing technology that is approachingcompetitiveness with traditional methods.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are part of the specification. The illustratedexamples are given merely for illustration, and do not limit the scopeof the claims.

FIG. 1 is a diagram of a system for forming a multiple layer object froma high melting temperature polymer according to an example of theprinciples described herein.

FIG. 2 is a diagram of a system according to one example consistent withthe principles described herein.

FIG. 3 is a flowchart showing a method of forming a consolidated partfrom high melting temperature polymer particulate according to anexample of the principles described herein.

FIG. 4 shows top view of a layer of polymer particulate with both theconsolidated zone that will form the part and the heat reservoirsaccording to one example of the principles described herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements. The figures are not necessarilyto scale, and the size of some parts may be exaggerated to more clearlyillustrate the example shown. Moreover, the drawings provide examplesand/or implementations consistent with the description; however, thedescription is not limited to the examples and/or implementationsprovided in the drawings.

DETAILED DESCRIPTION

Three dimensional printing has been able to produce figures usingpolymers. These figures often lack mechanical strength due to thepolymers used. In some cases, figures have been produced using threedimensional printing and then used to cast metal parts, for exampleusing a lost wax process. This has sometimes been more cost effectivethan machining parts but overall the increased number of operations anddifferent technologies (printing and casting) used have slowed adoptionof this approach.

Material science has also provided a solution in the form of new, highmelting temperature polymers. High melting temperature polymers(“HTPs”), also called structural polymers and/or engineering polymers,have high mechanical strengths, often on the order of metal parts formedfrom aluminum or low grade steel, low creep, and high stiffness. Forpurposes of this specification, HTPs are polymers with meltingtemperatures of at least 250 degrees C. HTPs may have less ductilitythan traditional metal parts and their creep strength is generallylower. However, unlike metals, HTPs may be molded. Molding of formerlymetal components from HTPs has allowed cost savings over machinedcomponents in many designs. Molding offers low per piece cost, verytight tolerances, high reproducibility with low part to part variation,excellent throughput, and other advantages over machined metal parts.However, molding HTPs is difficult, in part because of the hightemperature used to melt the HTP for molding, the higher viscosities andpressures involved, etc. Nevertheless, molded HTP parts have seenincreasing use in mechanically demanding applications.

Molding High melting Temperature Polymers (“HTPs”) uses molds, generallyeither aluminum or steel. Preparing molds, molding parts, adjusting themolds, and molding additional parts in order to produce a desired partcan be time consuming and expensive. This may make molding impracticalwhen a design is not yet fixed for the part. Often this has meant theuse of either machined metal parts and/or machined HTP parts for smallbatch and/or prototyping applications. This avoids the time and cost ofmold development while the part design is being finalized but still hashigh machining costs and substantial material waste.

Developing the ability to form 3D printed parts from high meltingtemperature polymers would provide 3D printed parts with greaterstrength and toughness than other 3D printed polymers. 3D printing is atechnology that is well suited to small runs of parts and fordevelopment/design testing, including forming min spec and max spectesting for validation studies, etc. Such parts reduce productdevelopment cycle times, reduce costs, and/or decrease project risk.

Printing three dimensional parts from HTPs has additional challengescompared with printing lower melt temperature polymers. For example, thehigher melting temperatures of the polymers can be damaging to thecomponents of the system. This may include the bed and spreader. Thismay include the fluid ejection head. Reaching higher temperaturesimplies greater energy input into the part. Greater temperatures alsoproduce greater temperature differentials and greater thermal stresses.Control may become more challenging due to the greater heat flux into,within, and out of the system. The fluid ejection head may experiencegreater wear, greater material accumulation in the nozzles and surfaceof the fluid ejection head. The higher temperatures and greater heatflux may impact the stability of fluid in the fluid ejection head.

The interaction between a deposited fusing and/or masking agent and thesystem becomes more challenging when dealing with high meltingtemperature polymers. Fluid ejection heads may use a solvent, forexample, water, to convey the material to the surface. The solvent thenevaporates and leaves the material behind on the surface. In a thermalinkjet (TIJ), a heater forms a gas bubble by evaporating the solvent,the gas bubble then pushes the fluid droplet out of the fluid ejectionhead toward the target. The drying time of the solvent on a surface maybe modified by heating and/or cooling. The drying time may also bemodified by use a more volatile solvent and/or solvents. The drying timemay be extended by adding a humectant, such as glycerol.

When depositing a fusing agent onto a surface of high meltingtemperature polymer particles, some additional challenges becomeapparent. The droplet containing the fusing agent contains liquid, forexample water, that makes thermal inkjet ejector function. However, thepolymer particles contacted by the droplet are at a temperature wellabove the boiling point of the liquid. This may result in the dropletscattering upon impact as the liquid turns to vapor. However, it hasbeen found that, if the temperature of the polymer particles isincreased further, a stable regime is reached where the polymerparticles hold together and deposition of the fusing agent can beaccomplished.

Another novel element is using a colder forming environment and heatingportions of the top layer of polymer particles. This allows the use ofless expensive materials for the system components. The polymerfunctions as an insulator, allowing a thermal gradient to be maintainedbetween the newly consolidated portion in the top layer of theaccumulating part and the environment. In order for this to work, theprocess of applying a layer, patterning with the fusing agent, andexposing to the radiation (heat) source needs to be accomplishedrelatively quickly. Otherwise, the heat loss is greater and theconsolidated areas may drop below the solidification temperature.Solidification may introduce warping and buckling making applyingadditional layers more difficult. Warping and buckling are disruptive toautomated and semi-automated methods of layer formation.

One way to slow the cooling of the top layer of polymer particles is toform areas in the layer to serve as heat reservoirs. This is done byapplying fusing agent to portions of the top layer that will not beincorporated into the part. These areas may be given a lowerconcentration of fusing agent. Accordingly, when flood irradiation isapplied, the heat reservoirs heat as well. The heat reservoirs reducethe thermal gradient between the parts of the top layer that will becomethe formed part and the areas that will not be part of the formed parts.Because heat transfer is dependent on the temperature difference,reducing the temperature differential reduces the flow of heat out fromthe formed part. In another sense, adding additional heat into the toplayer in the form of heat reservoirs keeps the consolidated areas of thetop layer at a higher temperature for a longer period of time. Thisextended time allows a new top layer to be formed before the meltedpolymer particles formed reach the solidification temperature. Addingthe new layer on top serves to insulate and support the forming part,reducing the thermal gradients that induce warping and providingmechanical support to resist warping. This allows the forming ofconsolidated components made from high melting temperature polymerswithout raising the environment to near the polymer Tm, without heatingall the new layer of polymer particulate, and/or without usingcomponents hardened to support a higher bed temperature.

Among other examples, the present specification and figures disclose asystem for forming a multiple layer object, the system including: aspreader to form a layer of polymer particles, the polymer particleshaving a melting temperature (Tm) of at least 250° C.; a fluid ejectionhead to selectively deposit a first fusing agent on a first portion ofthe layer and selectively deposit a second fusing agent on a secondportion of the layer, wherein the fluid ejection head does not deposit afusing agent on a third portion of the layer; and a heat source to heatthe first portion and second portion, wherein the first portion is partof the multiple layer object and the second portion is not part of themultiple layer object and the second portion raises a temperature ofpolymer particles in a subsequent layer.

This specification also discusses, a system including: a spreader toform layers of polymer particles, the polymer particles having a meltingtemperature (Tm) of at least 250° C.; a fluid ejection head toselectively deposit a fusing agent on a top layer of the layers ofpolymer particles; a bed heater to heat a working area of the system tono more than 10 degrees centigrade below the Tm of the polymerparticles; and a radiation source to selectively heat the top layer,wherein spreading a new layer on top of the layers of polymerparticulate, applying the fusing agent to the new layer, and heating thenew layer with the radiation source are accomplished such that thetemperature of the top layer remains above a solidification temperature(Ts) of the polymer particles until the top layer is covered by the newlayer.

This specification also discusses a method, the method including: in abed area of a first temperature, heating a top layer of polymerparticles of a multiple layer assembly to between a second temperatureand a third temperature; and while a top surface of the top layer isbetween the second temperature and the third temperature, selectivelyapplying a fusing agent to the top surface of the top layer using afluid ejection head; wherein the third temperature a melting temperature(Tm) of the polymer particles as determined by differential scanningcalorimetry (DSC) as a largest point of a melting peak, the secondtemperature is a temperature wherein the polymer particles become tackysuch that deposited agent does not displace the particles, and the firsttemperature is at least 50 degrees centigrade below Tm.

As used in the present specification and the appended claims, the termmelting temperature (Tm) is defined by the largest melting peak in adifferential scanning calorimetry scan of the relevant polymer. Becauseof the high thermal gradients, small scale, and factors, the effectiveTm may differ from a steady state, and/or slow scan speed meltingtemperature. Similarly, the solidification temperature (Ts) is thelargest solidification peak when cooling the polymer. In high meltingtemperature polymers, it is not uncommon for the melting temperature(Tm) and the solidification temperature (Ts) to be separated with aworking area in between where the material may be solid and/or liquiddepending on the processing history. The keeping the formed portion ofthe component between Tm and Ts may reduce stresses in the formed part.Slowing the transition through the Ts may reduce the stresses lockedinto the solidified component. A potentially useful analogy is quenchingvs. annealing in metal parts where a slower transition with smallerthermal gradients allows more time for the system to relieve stress,although clearly the mechanisms are quite different.

As used in this specification and the associated claims, the term “bedtemperature” refers to the temperature of the particulate in theparticulate layers that are not preferentially heated by energy absorbedby the fusing agent. These exclude the heat reservoir(s) and theconsolidated portion(s) of the particulate layer. The ability to providea gradient between the bed temperature and the consolidated areas allowsthe use of lower cost, more temperature sensitive components. It isfacilitated by the use of a rapid layer forming, patterning, and heatingcycle, for example, a rapid cycle associated with a multiple jet fusionprocess.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present apparatus, systems,and methods may be practiced without these specific details. Referencein the specification to “an example” or similar language means that aparticular feature, structure, or characteristic described in connectionwith that example is included as described, but may or may not beincluded in other examples.

Turning now to the figures, FIG. 1 is a diagram of a system (100) forforming a multiple layer object from a high melting temperature polymeraccording to an example of the principles described herein. The system(100) including: a spreader (120) to form a layer of polymer particles(110), the polymer particles (110) having a melting temperature (Tm) ofat least 250° C.; a fluid ejection head (130) to selectively deposit afirst fusing agent (132) on a first portion of the layer and selectivelydeposit a second fusing agent (134) on a second portion of the layer,wherein the fluid ejection head does not deposit a fusing agent (132,134) on a third portion of the layer, and a heat source (140) to heatthe first portion and second portion, wherein the first portion is partof the multiple layer object and the second portion is not part of themultiple layer object and the second portion raises a temperature ofpolymer particles (110) in a subsequent layer.

The system (100) is a system for forming a multiple layer object from ahigh melting temperature polymer. In this system (100), a layer ofpolymer particles (110) is formed and then selectively consolidated toform a layer of the object. Another layer of polymer particles (110) isapplied and the process repeated. The object is built up layer by layeruntil the desired thickness is reached. This approach has someadvantages over providing the material for the object throughdeposition. The use of consolidated polymer particles (110) may havehigher throughput and/or quicker layer times. The use of consolidatedpolymer particles (110) may have thicker layers, reducing the totalobject forming time. The use of consolidated polymer particles (110) maymake producing distributions of color, composition, strength, etc.within the formed object more difficult compared with a system wheredifferent materials are deposited to build up the component. The use ofa consolidated polymer particle (110) approach also uses a spreader(120) to form the layer of polymer particles (110).

The polymer particles (110) provide the material to form the multiplelayer object. The polymer particles (110) include high meltingtemperature polymer. High melting temperature polymers may be polymerswith a melting temperature above 250° C. High melting temperaturepolymers may be polymers with a melting temperature above 300° C. Highmelting temperature polymers may be polymers with a melting temperatureabove 325° C. Examples of high melting temperature polymers include, butare not limited to: Fluorinated ethylene propylene (FEP, Tm of 260° C.);Perfluoroalkoxy alkane (PFA, Tm of 260° C.); Polyamide 6,6 (Nylon 6,6)(PA 6,6, Tm of 265° C.); Polyphenylene sulfide (PPS, Tm of 280° C.);Polyamide 4,6 (PA 4,6, Tm of 280° C.); Polyphthalamide (PPA, Tm of 310°C.); Liquid crystal polymer-Glass composite (e.g. Zenite) (LCP, Tm of319° C.); Polytetrafluroethylene (PTFE, Tm of 327° C.);Polyetherketoneketone (PEKK, Tm of 337° C.); Polyether ether ketone(PEEK, Tm of 343° C.); and Polyaryletherketones (PAEK, Tm of 345° C.);and/or Liquid crystal polymers (LCP, Tm of 420° C.).

The polymer particles (110) may be of a single polymer, for example,PEEK. The polymer particles (110) may be a mixture of polymers, e.g. PA6,6 and PA 4,6. The polymer particles (110) may be in a singledistribution. The polymer particles (110) may include multiple sizedistributions, for example, a larger mean size distribution and asmaller mean size distribution to create a bimodal distribution. In someexamples, the smaller particles are formed with a higher meltingtemperature (Tm) polymer. In some examples, the smaller particles areformed from a lower melting temperature polymer. The use of a bimodalsize distribution may achieve higher density parts than the use of asingle size distribution.

The polymer particles (110) may be mixed with other components to modifythe formed multilayer object. Care and experimentation may be needed asadding additional components, e.g. a flow agent and/or a colorant, mayimpact the performance of the polymer particles (110). The tackiness ofthe polymer particles (110) is sensitive to additional components. Thisis consistent with a working theory that the tackiness at highertemperatures is driven by the behavior of amorphous portions of a semicrystalline high melting temperature polymer. If the crystallineportions remain intact in the tacky particles, then a very thin surfacecomponent is able to effectively interact with other particles. However,the thinness of the interacting layer may allow this behavior to bedisrupted by relatively small amounts of secondary materials.

The spreader (120) is used to form a layer of polymer particles (110).The spreader (120) may include a feed to provide additional particulateto form the layer of polymer particles (110). The spreader (120) mayinclude a vibrating component to distribute and/or compact the layer ofpolymer particles (110). The spreader (120) may make a single pass toform the layer of polymer particles (110). The spreader may makemultiple passes to form the layer of polymer particles (110). In someexamples, the subsequent passes increase the density of the layer ofpolymer particles (110). The spreader (120) may be automatic. Thespreader (120) may be semi-automatic. The spreader (120) may be manuallyoperated by a user.

The spreader (120) may form layers of polymer particles (110) that areof a uniform depth. The spreader may vary the depth of the formed layerof polymer particles (110) as a function of location in the part,location in the bed, and/or feature resolution. In some examples, thespreader (120) uses a first thickness for the initial layer and/or theinitial few layers and then changes to a second thickness for subsequentlayers.

The spreader (120) may be a roller. The roller may rotate in thedirection of motion and/or opposite the direction of motion. In someexamples, the roller compacts and/or increases the density of the layerof polymer particles (110). The spreader (120) may be a pusher. Thespreader (120) may include a leveling blade. The spreader (120) mayinclude multiple rollers, for example, a first roller to level and as asecond roller to compact.

The spreader (120) may provide additional functionalities besidesspreading of the polymer particles (110). The spreader may pattern thepolymer particles (110). The spreader (120) may apply polymer particles(110). The spreader may heat and/or cool the layer of polymer particles(110). The spreader (120) may be combined with the fluid ejection head(130). In some examples, the operation of spreading and applying thefirst fusing agent (132) and/or the second fusing agent (134) isperformed in a single pass.

The spreader (120) may include multiple particle feeds. In someexamples, the spreader (120) provides a first distribution of particlesfor the initial layer and a second distribution of particles insubsequent layers. The spreader (120) may apply a first distribution ofparticles on a first pass and a second distribution of smaller particleon a second pass. The spreader (120) may apply a first distribution ofsmaller particles near the bottom of the layer and a second distributionincluding more, larger particles near the top of the layer of polymerparticulate (110).

The fluid ejection head (130) ejects the first fusing agent (132) andthe second fusing agent (134) onto the layer of polymer particles (120).The fluid ejection head (130) may be part of a printbar. The fluidejection head (130) may be static and/or move relative to a formingarea. The fluid ejection head (130) may include a plurality of solutionsfor patterning on the polymer particles (110). The fluid ejection head(130) may contain a fusing agent (132, 134). The fluid ejection head mayinclude a masking fluid to selectively reduce absorption of theradiation from the radiation source (140).

The first fusing agent (132) increases the energy absorbed by theradiation source (140). The first fusing agent (132) may absorb a broadspectrum of electromagnetic radiation. The first fusing agent (132) mayabsorb a narrow wavelength of electromagnetic radiation. The firstfusing agent (132) may be carried in a solvent, where the solvent actsas the propellant in the fluid ejection head. For example, the firstfusing agent (132) may be in water. The first fusing agent may be mixedwith a humectant, an anti-kogation agent, a detergent, an ion source, apH modifier, a chelator, and/or combinations thereof.

The second fusing agent (134) increases the energy absorbed from theradiation source (140). The second fusing agent (134) may be the sameagent as the first fusing agent (132) but at a different concentrationin solution. The second fusing agent (134) may be the same formulationas the first fusing agent (132) but applied at a different density onthe polymer particles (110).

The first fusing agent (132) and the second fusing agent (134) mayinclude different materials. Fusing agents (132, 134) may include:carbon black, platinum black, titanium black, ivory black, black ironoxide, graphite, aniline black, and/or anthraquinone black. The firstfusing agent (132) and second fusing agent (134) may include any nearinfrared absorbing dyes and/or pigments. These may include materialswhich strongly absorb in the infrared and/or visible regime. Some otherexamples include doped cesium-tungsten oxide pigments and metalditholene chemical dyes. Further discussion of fusing agents (132, 134)may be found in PCT/US2017/016681, “Fusing Agent including a Metalbis(Dithiolene) Complex” by Olubummo, which is incorporated byreference.

The radiation source (140) provides energy that is preferentiallyabsorbed by the portions of the layer of polymer particles (110) thathave been treated with the first fusing agent (132) and/or the secondfusing agent (134). The untreated areas of the layer of polymerparticles (110) may absorb energy from the radiation source (140). Theuntreated polymer particles (110) may absorb less than 10% of the energyof the radiation from the radiation source falling on the untreatedpolymer particles (110). That is to say, in some examples, more than 90%of the radiation is reflected and/or transmitted by the untreatedpolymer particles (110).

The radiation source (140) may be a pulsed irradiation light source.Pulsed irradiation light sources are capable of applying large amountsof light in a relatively short period of time. This makes pulsedirradiation light sources a useful energy source for high throughputoperations such as three dimensional forming. Pulsed irradiation lightsources may also be used in a flood mode, rather than as a point source,for example, like a laser. Irradiating the entire treatment areasimultaneously provides throughput advantages as well as uniformityadvantages. Simultaneous treatment of the layer of polymer particles(110) may reduce the internal stresses in the consolidated part.Simultaneous treatment may produce more uniform heating and cooling.

Pulsed irradiation light sources may be monochromatic. Pulsedirradiation light sources may have a distribution of wavelengths,including wavelengths in the infrared, visible, and/or ultravioletfrequencies. Pulsed irradiation light sources may use a light emittingdiode (LED), an array of LEDs, plasmas, filaments, and/or othercomponents to generate the electromagnetic radiation used to heat thepolymer particles (120).

The radiation source (140) may provide the radiation as a single pulse.The radiation source (140) may provide the radiation as a series ofpulses. The pulses may be of the same wavelength and/or energy. Thepulses may vary, for example, a first type of pulse may be used to heatthe polymer particles (120) and a second pulse with a different energy,wavelength, duration, frequency, spectrum, and/or other property may beused after the first pulse. The wavelength of the radiation provided bythe radiation source may be selected based on a preferential absorbancefrequency of the fusing agent, for example, based on a bond found in thefusing agent but not found in the polymer particles (110). Similarly, aheating pulse and/or maintenance pulse may be applied that is notdependent on the preferential absorbance of the fusing agent. Selectinga wavelength that preferentially interacts with a characteristicchemical bond in the polymer particles (110) may be useful.

FIG. 2 is a diagram of a system according to one example consistent withthe present specification. The system (100) includes: a spreader (120)to form layers of polymer particles (110), the polymer particles havinga melting temperature (Tm) of at least 250° C.; a fluid ejection head(130) to selectively deposit a fusing agent (132, 134) on a top layer ofthe layers of polymer particles (110); a bed heater (250) to heat aworking area of the system to no more than 10 degrees centigrade belowthe Tm of the polymer particles (110); and a radiation source (140) toselectively heat the top layer of polymer particles (110), whereinspreading a new layer on top of the layers of polymer particles (110),applying the fusing agent (132, 134) to the new layer, and heating thenew layer with the radiation source (140) are accomplished such that thetemperature of the top layer remains above a solidification temperature(Ts) of the polymer particles (110) until the top layer is covered bythe new layer.

The system (100) is a system for forming consolidated parts from polymerparticles (110). The system (100) uses a fusing agent (132, 134) toselectively heat portions of a layer of polymer particles (110).

The bed heater (250) provides heat to the part forming area where thepart is being fused. The bed heater (250) may include a temperaturesensor. The bed heater (250) may include a controller, for example, aproportional, integral, derivative (PID) controller. The bed heater(250) may use a predefined heating profile to accommodate the dynamicprocess of part forming. In some examples, the predefined heatingprofile is refined over multiple instances of a common part design.

The bed heater (250) may include heating coils, for example, electricalresistive heating elements, steam lines, etc. The bed heater (250) mayinclude an upper limit, for example, the bed heater (250) may be a heatexchanger where the input fluid into the heat exchanger is below to sometemperature relative to the melting temperature of the polymer particles(110).

FIG. 3 shows a flowchart for a method (300) of forming a multiple layerassembly using a polymer with a melting temperature (Tm). The method(300) includes: while keeping a bed area at least 10 degrees centigradebelow Tm, heating a top layer of polymer particles (110) of a multiplelayer assembly to a first temperature, where the first temperature isabove a temperature at which the polymer particles (110) becomesufficient tacky to resist displacement by a deposited agent (390); andwhile a top surface of the top layer is at the first temperature,selectively applying a fusing agent (132, 134) to the top surface of thetop layer using a fluid ejection head (130)(392).

The method (300) is a method (300) of forming a multiple layer assemblyusing a polymer with a melting temperature (Tm). The polymer particles(110) may be a semi crystalline high melting temperature polymer with amelting temperature of Tm. The Tm may be determined using the largesmelting peak on a differential scanning calorimetry (DSC) measurement ofthe polymer particles (110).

The method (300) includes, while keeping a bed area at least 10 degreescentigrade below Tm, heating a top layer of polymer particles (110) of amultiple layer assembly to a first temperature, where the firsttemperature is above a temperature at which the polymer particles (110)become sufficient tacky to resist displacement by a deposited agent(390. Getting the layer of polymer particles (110) to become tacky so asto resist displacement allows patterning with the fusing agent withoutdisrupting the layer. The presence of this tacky zone between theboiling point of the fusing agent (132, 134) solution and the meltingtemperature of the polymer particulate increases dimensional control ofthe formed object.

The method (300) includes, while a top surface of the top layer is atthe first temperature, selectively applying a fusing agent (132, 134) tothe top surface of the top layer using a fluid ejection head (130)(392).Selective application of the fusing agent (132, 134) enables selectiveheating of the areas to form the consolidated part while other areasremain at a lower, bed temperature to avoid damage to the system (100).The use of the polymer particulate to insulate the forming area and theability to rapidly form a layer, patterning the layer, and selectiveheat the desired portions allow forming a consolidated part from apolymer with a high melting temperature without hardening the system.This dynamic control approach offers equipment cost and throughputadvantages over systems that bring the bed to near the meltingtemperature of the polymer particulate (110).

At low temperatures, the deposition of fluids with onto materials isrelatively straightforward. The fluid is placed in an inkjet. The inkjetactivates and expels a droplet of fluid to a substrate. In a thermalinkjet (TIJ), the droplet is expelled by forming a gas bubble whichexpands and ejects the fluid. In a piezoelectric inkjet (PIJ) apiezoelectric actuation has a potential applied that produces a shapechange that expels the droplet. The droplet lands on a substrate.Solvent in the fluid then dry and deposited material remains on thesurface. In some cases, the surface is heated, for example, with asecondary heater to drive off the solvent and/or polymerize thedeposited material.

However, as the surface temperature increases and passes a boiling pointof the mixture, the behavior may change. When a droplet is dropped ontoa surface that is higher temperature than the boiling point of thedroplet, the contact with the surface may form a vapor layer that liftsand propels the droplet chaotically around the surface. A common exampleof this is a droplet of water on a hot pan. Thus, when the droplet landson the layer of polymer particles (110) which are above the boilingpoint of the droplet, the motion of the droplet may disrupt the layer ofpolymer particles as the droplet darts back and forth across the surfaceand/or from pressure build-up from evaporating gases. Further, the finallocation of the fusing agent (132, 134) in the droplet is deposited at aposition that is a random walk from the targeted location. This mayprevent effective patterning of the fusing agent (132, 134) on the layerof polymer particles (110). Without patterning, the ability toselectively apply heat using the radiation source (140) is impaired.

With high melt temperature polymers, it has been found that once thepolymer particles (110) reach a sufficiently high temperature (but stillbelow the Tm), the polymer particles (110) become tacky. The result isthat deposited droplets do not disrupt the layer of polymer particles(110) and the fusing agent (132, 134) may be effectively patterned onthe polymer particles (110). While not wishing to be bound by anyparticular theory, it is believed that the amorphous portions of thesemi crystalline polymer particles (110) are interacting and thisinteraction provides the tackiness between polymer particles (110)holding them together. This may occur substantially below the Tm wherethe crystalline portions of the polymer particles (110) are finallydisrupted. In some examples, the second temperature is 70 degrees C.below Tm. In some examples, the second temperature is 50 degrees C.below Tm. The second temperature may be 30 degrees C. below Tm. Thesecond temperature may be 20 degrees C. below Tm. Determination of thesecond temperature will depend on the polymer particles (110) includingtheir composition.

Components rated to 200° C. temperatures and/or 150° C. temperatures maybe produced from lower cost materials and/or methods than componentsthat much remain functional at, for example, 300° C. Instead ofhardening the system (100) with high temperature resistant, high costcomponents, this method localizes the high temperature operations withinthe bed area. This allows an operating temperature that doesn't useexpensive materials in order to assure the system remains functional.The polymers and environment may be kept sufficiently insulating topreserve the temperature gradient between the first temperature and thethird temperature.

In some examples, the first temperature is at least 100° C. less thanTm. In some examples, the first temperature is at least 50° C. less thanTm. In some examples, the first temperature is at least 30° C. less thanTm. In some examples, the first temperature is at least 10° C. less thanTm. In some successful experiments, the bed temperature was limited to180° C., while the Tm of the particulate consolidated in the top layerof polymer particulate (110) was 345° C. In other testing, a bedtemperature of 180° C. has been used to support a temperature of 450° C.in the areas of the polymer to be consolidated. Temperature differencesof up to approximately 400° C. between the bed temperature andtemperature of the consolidated polymer particulate (110) areachievable. Clearly, large temperature differences have their associatedchallenges. For example, the use of multiple layers of heat reservoirsand/or thicker layers including more and/or larger heat reservoirs maybe needed. The greater temperature difference makes control of coolingrates more challenging. Higher temperatures in an oxygen environment(e.g. air) may result in oxidation, degradation, and/or decomposition ofsome polymers. The use of an inert and/or vacuum environment to reduceconvection may facilitate higher temperature. In practice, a differenceof 200° C. would allow forming of a variety of high melting temperaturepolymers, e.g. PEEK and most of the example polymers discussed above,using a bed temperature that does not have heat tolerances above 150° C.This lower bed temperature may cut the system cost compared with systemsdesigned to support high bed temperatures. In some examples, the systemmay be one half to one quarter the cost of a temperature hardenedsystem. This coupled with the throughput advantages provided by multiplejet fusion make 3D printed parts from HTPs affordable and practical formany applications that were too expensive using other methods andequipment.

The bed temperature may be limited to 120° C. The bed temperature may belimited to 150° C. The bed temperature may be limited to 180° C. Otherbed temperatures may be selected depending on the temperature tolerancesof the system (100) and components of the system (100) in the bed area.Temperature differences up to approximately 400° C. between the bedtemperature and the peak temperature of the polymer layer (110) may besupported with proper layer patterning and diligent control. The abilityto rapidly form, pattern, and heat the top layer is part of achievinglarger temperature differences and avoiding excessive cooling whileforming the object.

FIG. 4 shows top view of a layer of polymer particulate (110) with boththe consolidated zone (460) that will form the part and the heatreservoirs (470) according to one example of the principles describedherein.

FIG. 4 shows a consolidated zone (460) in the shape of a tensile testspecimen (a.k.a. a “dogbone”). Heat reservoirs (470) are located oneither side of the narrower portion of the test specimen. The additionof the heat reservoirs (470) near the narrower portion of theconsolidated zone (460) helps to equalize the cooling rate of the endsof the test specimen and the center of the test specimen. The extra heatprovided by the heat reservoirs (470) also slows the cooling rate of thelayer overall, for example, to keep the consolidated zone (460) and/orthe heat reservoirs (470) above the solidification temperature (Ts) ofthe polymer making up the polymer particles.

Clearly, the shown example is a very simple application of the heatreservoir (470) concept. Heat reservoirs (470) may be placed based onunderstanding of heat fluxes. In some examples, the system (100)providing information to the fluid ejection head (130) includes aprocessor that calculates the positions, size, and/or fusing agentdensity to control the cooling rate and uniformity of the layer ofpolymer particles (110) including the consolidated zone (460).

In some examples, heat reservoirs (470) are placed in differentlocations on adjacent layers of the multiple layers used to form theconsolidated part. In some examples, heat reservoirs (470) are placed onsome layers and not placed on other layers. For example, heat reservoirs(470) may be placed on every other layer, every third layer, two out ofevery three layers, etc. The heat reservoirs (470) may be very small,for example, as small as a single droplet of fusing agent (132, 134)applied to the layer of polymer particles (110). In some examples, abroad region of the layer of polymer particles (110) has hundreds ofsmall and/or single droplet heat reservoirs (470). In some examples, thefirst layer and/or the first several layers of the multiple layers ofpolymer particulate (110) may include a patterning of heat reservoirs(470) without a consolidated region (460). Once a base region ofsuitable temperature has been formed, the consolidated region may bepatterned in.

The preceding description has been presented to illustrate and describeexamples of the principles described. This description is not intendedto be exhaustive or to limit these principles to any precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching.

What is claimed is:
 1. A system for forming a multiple layer object, thesystem comprising: a spreader to form a layer of polymer particles, thepolymer particles having a melting temperature (Tm) of at least 250° C.;a fluid ejection head to selectively deposit a first fusing agent on afirst portion of the layer and selectively deposit a second fusing agenton a second portion of the layer, wherein the fluid ejection head doesnot deposit a fusing agent on a third portion of the layer; and a heatsource to heat the first portion and second portion, wherein the firstportion is part of the multiple layer object and the second portion isnot part of the multiple layer object and the second portion raises atemperature of polymer particles in a subsequent layer.
 2. The system ofclaim 1, wherein the fusing agent is applied with a first density on thefirst portion of the layer and the fusing agent is applied with a seconddensity on the second portion of the layer.
 3. The system of claim 1,wherein the first portion of the layer has a first density of the fusingagent at an edge of the portion and a second density of the fusing agentat a center of the portion.
 4. The system of claim 1, wherein the firstfusing agent and the second fusing agent comprise a shared functionalmaterial.
 5. The system of claim 1, wherein the heat source applies heatto the first portion, second portion, and third portion simultaneously.6. The system of claim 1, wherein the heat source applies radiationuniformly to the first portion, second portion, and third portion of thelayer.
 7. The system of claim 1, wherein the first portion fuses due toapplication of heat by the heat source and the second portion does notmelt due to application of heat by the heat source.
 8. A system, thesystem comprising: a spreader to form layers of polymer particles, thepolymer particles having a melting temperature (Tm) of at least 250° C.;a fluid ejection head to selectively deposit a fusing agent on a toplayer of the layers of polymer particles; a bed heater to heat a formingarea of the system to no more than 10 degrees centigrade below themelting temperature of the polymer particles; and a radiation source toselectively heat a portion of the top layer containing the fusing agent,wherein spreading a new layer on top of the layers of polymerparticulate, applying the fusing agent to the new layer, and heating thenew layer with the radiation source are accomplished such that a meltedportion of the top layer remains above a solidification temperature (Ts)of the polymer particles until the top layer is covered by the newlayer.
 9. The system of claim 8, wherein the fusing agent is selectivelydeposited on a first portion that will form a consolidated part and on asecond portion that will not be part of the consolidated part.
 10. Thesystem of claim 9, wherein the second portion is maintained above thesolidification temperature until the top layer containing thesolidification portion is covered with a new layer of polymer particles.11. The system of claim 8, wherein a polymer forming the polymerparticles is a semi-crystalline polymer.
 12. The system of claim 11,wherein a top surface of the top layer of polymer particles prior toselective application of the fusing agent has a temperature from asolidification temperature (Ts) to a melting temperature (Tm).
 13. Amethod of forming a multiple layer assembly using a polymer with amelting temperature (Tm), the method comprising: while keeping a bedarea at least 10 degrees centigrade below the melting temperature (Tm),heating a top layer of polymer particles of a multiple layer assembly toa first temperature, where the first temperature is above a temperatureat which the polymer particles become sufficient tacky to resistdisplacement by a deposited agent; and while a top surface of the toplayer is at the first temperature, selectively applying a fusing agentto the top surface of the top layer using a fluid ejection head.
 14. Themethod of claim 13, further comprising heating a portion of the toplayer using radiation absorbed by the selectively applied fusing agent.15. The method of claim 14, further comprising: forming a new top layerover the top layer, and repeating heating, selectively applying, andforming to build up a multiple layer solidified part while the bedtemperature remains at least 10 degrees centigrade below the meltingtemperature (Tm).